mdadm enable bitmap to speed up rebuilds

Have you ever unplugged the wrong drive and then had to rebuild the entire array?  It may not be a big deal in some ways but it does make your system vulnerable until the rebuild is done.

Many distros often enable the "bitmap" feature and this basically keeps track of what parts need to be resynced in the case of a temporary removal of a drive from the array, this way it only needs to sync what has changed.

To enable bitmap to speed up rebuilds and sync only the changed data

mdadm --grow /dev/md12 --bitmap=internal

Once you do that when you do a cat /proc/mdstat you\'ll see the change (with bitmap: being mentioned):

md12 : active raid1 sde1[0] sdd1[1]
      1953511936 blocks [2/2] [UU]
      bitmap: 233/233 pages [932KB], 4096KB chunk

 

Here's what happens when unpulgging a drive from  a RAID 1:

[46911.392690] raid1: sde1: rescheduling sector 1953247352
[46911.425512] raid1: Disk failure on sde1, disabling device.
[46911.425513] raid1: Operation continuing on 1 devices.
[46911.425529] raid1: sdd1: redirecting sector 1953247352 to another mirror
[46911.544209] RAID1 conf printout:
[46911.544213]  --- wd:1 rd:2
[46911.544215]  disk 0, wo:1, o:0, dev:sde1
[46911.544216]  disk 1, wo:0, o:1, dev:sdd1
[46911.560862] RAID1 conf printout:
[46911.560864]  --- wd:1 rd:2
[46911.560867]  disk 1, wo:0, o:1, dev:sdd1


When readding it, they were both still sync'd almost instantly, this is because no changes were really made.

md12 : active raid1 sdf1[0] sde1[2](F) sdd1[1]
      1953511936 blocks [2/2] [UU]
      bitmap: 0/233 pages [0KB], 4096KB chunk


Tags:

mdadm, enable, bitmap, rebuildshave, unplugged, rebuild, array, distros, quot, feature, resynced, removal, sync, rebuilds, dev, md, proc, mdstat, ll, active, raid, sde, sdd, uu, kb, chunk, unpulgging, rescheduling, sector, disk, disabling, continuing, devices, redirecting, conf, printout, wd, rd, wo, readding, instantly, sdf,

Latest Articles

  • virt-resize: error: libguestfs error: could not create appliance through libvirt.
  • Asterisk Does Not Retry When Authentication Fails
  • Linux Debian Ubuntu How To Install PEPPER Faster and Latest Adobe Flash Player in Firefox
  • How To Speed Up Linux Ubuntu and Debian Based Computers By Improving CPU Performance and Changing the CPU Governor
  • Convert data or file to base64 on a single line
  • Linux Mint Ubuntu Debian radeon slow 2D performance issues radeon_dp_aux_transfer_native: 158 callbacks suppressed
  • mdadm: super0.90 cannot open /dev/sdb1: Device or resource busy mdadm: /dev/sdb1 is not suitable for this array.
  • How To Install NextCloud on Centos 7 and Centos 8
  • AH01630: client denied by server configuration:
  • ERROR: Could not find a version that satisfies the requirement PIL (from versions: none) ERROR: No matching distribution found for PIL
  • ZTE Camera Cannot Work unable to connect to camera. Camera has been disabled becaue of security policies or is being used by other apps
  • QEMU KVM how to boot off a physical CD/DVD/BDROM Drive
  • How To Install OpenProject on Centos 7 Step-by-Step Guide
  • Ubuntu Debian Linux Cannot Install Wine Solution - wine1.6 : Depends: wine1.6-i386 (= 1:1.6.2-0ubuntu14.2) but it is not installable wine1.4 : Depends: wine1.6 but it is not going to be installed
  • How To Install python 3.4 3.5 and up on Linux with wine - Working Solution
  • using Xvfb on virtual remote ssh server to have X graphical programs work
  • ssh Received disconnect from port 22:2: Too many authentication failures
  • named bind errors - DNSKEY: unable to find a DNSKEY which verifies the DNSKEY RRset and also matches a trusted key for '.'
  • OpenVZ vs LXC DIR mode poor security in LXC
  • httpd: Syntax error on line 221 of /etc/httpd/conf/httpd.conf: Syntax error on line 6 of /etc/httpd/conf.d/php.conf: Cannot load modules/libphp5.so into server: /lib64/libresolv.so.2: symbol __h_errno, version GLIBC_PRIVATE not defined in file libc.s